Answer:
The correct answer would be d. thymus.
The thymus is a specialized lymphoid organ of an immune system.
It serves as the site for training and maturation of T-lymphocytes or T cells.
It is composed two identical lobes each containing outer region termed as cortex and inner region termed as medulla.
T-cells are first trained and selected in the cortex region via positive selection. In this, T cells which are able to bind to foreign antigens are selected and rest are degraded.
The selected T cells then move in the medulla region where they are selected by negative selection. In this, the T cells which binds to self-antigens are degraded and rest survive to become functional T cells.
Answer:
In the absence of decomposers, soil, air, and water would not be replenished, and all the nutrients present would soon get exhausted. Hence, the cyclic process of life and death would be disrupted and life would come to an end.
Answer:
b. Only about one-half of the world's population relies on sunlight to maintain adequate vitamin D nutrition
Explanation:
Dark skin pigments slow down the synthesis of vitamin D, so black people need to spend more time in the sun to absorb enough vitamin D, so the letter A is incorrect.
Prolonged exposure to sunlight degrades the precursor of vitamin D, whereas prolonged exposure to sunlight produces vitamin D3, which acts to regulate heart function and blood pressure. With this we can conclude that the letter C is also incorrect.
Vitamin D deficiency is not caused by calcium deficiency, on the contrary, vitamin D deficiency is a cause of calcium deficiency. In addition, summer vitamin D synthesis stocks are usually not sufficient to meet summer vitamin D requirements. That is why the letter D is also incorrect.
We can conclude, then, that the correct answer is the letter B. The main source of vitamin production is through sun exposure, because type B ultraviolet rays (UVB) are able to activate the synthesis of this substance. Some foods, especially fatty fish, are sources of vitamin D, but the sun is responsible for 80 to 90% of the vitamin the body receives. It can also be produced in the laboratory and given as a supplement when there is a deficiency and for the prevention and treatment of a variety of diseases.
Answer:
when food is scarce slime molds gather to form one structure. They are slimy and they move towards food and water.
Explanation:
